Site-made roof trusses are either hand made timber roof trusses connected with bolts and nails OR site application nail plates at the node points.
Pre-manufactured trusses are pre-manufactured timber roof trusses based on SANS 10243 and connected with engineering system provided nail plates as per design.
Site-made trusses would have had to, as a rational design, be designed by a registered Professional Competent Person. Girders for hips & valleys must be designed by an Engineer before manufacturing.
Pre-manufactured trusses are designed using the Engineering Software from one of the 4 accredited system members of the ITC-SA: Alpine Automation; International Truss Systems; MiTek Industries and Multinail South Africa.
Both site-made and pre-manufactured trusses have to be inspected for compliance with Regulation A19 of the National Building Regulations, the Design intent and specific regulations and specifications related to Timber Roof Trusses, where a Registered Professional Person as per the Engineering Council South Africa will take liability for the said structure.Once complying as per the Engineer, a Certificate of Compliance will be issued that will allow the owner to obtain an occupancy Certificate from the Local Municipality.
Statistics obtained by the Institute for Timber Construction South Africa show that 90% of site-made trusses do not comply with the relevant regulations and specifications as required by the National Building Regulations. This includes no rational designs and the use of non-structural timber members. They are found to be around ±20% more expensive than pre-manufactured timber roof trusses. Should there be any queries, you will generally have no avenue for remedy and will end in tedious and costly civil litigation! Any savings that your builder may have wrongly advised you of will be negated many times over!!
If these pre-manufactured trusses are erected by an accredited ITC-SA Roof Erector, you are guaranteed a roof structure that complies 100% and you have the peace of mind that, should you have any queries, there is an avenue for remedy via the ITC-SA’s disciplinary procedures for all its accredited members.